Different Ways to Remove all the Digits from String in Java

Given alphanumeric string str, the task is to write a Java program to remove all the digit from this string and prints the modified string.

Examples: 

Input: str = “GeeksForGeeks123”
Output: GeeksForGeeks
Explanation: The given string contains digits 1, 2, and 3. We remove all the digit and prints the modified string.

Input: str = “12Java”
Output: Java
Explanation: The given string contains digits 1 and 2. We remove all the digit and prints the modified string.

Method 1: Using String.toCharArray() method

1. Get the String to remove all the digit.
2. Convert the given string into a character array.
3. Initialize an empty string that stores the result.
4. Traverse the character array from start to end.
5. Check if the specified character is not digit then add this character into the result variable.
6. Now, print the result.

Below is the implementation of the above approach:

Java

// Java program to remove all the
// digit from string
class GFG {

    // Function to remove all the digit
    // from string
    public static String removeAllDigit(String str)
    {
        // Converting the given string
        // into a character array
        char[] charArray = str.toCharArray();
        String result = "";

        // Traverse the character array
        for (int i = 0; i < charArray.length; i++) {

            // Check if the specified character is not digit
            // then add this character into result variable
            if (!Character.isDigit(charArray[i])) {
                result = result + charArray[i];
            }
        }

        // Return result
        return result;
    }

    // Driver Code
    public static void main(String args[])
    {

        // Given alphanumeric string str
        String str = "GeeksForGeeks123";

        // Print the modified string
        System.out.println(removeAllDigit(str));
    }
}

Output

GeeksForGeeks

• Time Complexity: O(N)
• Auxiliary Space: O(N)

Method 2: Using String.charAt() method

1. Get the String to remove all the digit.
2. Initialize an empty string that stores the result.
3. Traverse the String from start to end.
4. Check if the specified character is not digit then add this character into the result variable.
5. Now, print the result.

Below is the implementation of the above approach:

Java

// Java program to remove all the
// digit from string
class GFG {

    // Function to remove all the digit
    // from string
    public static String removeAllDigit(String str)
    {
        String result = "";

        // Traverse the String from start to end
        for (int i = 0; i < str.length(); i++) {

            // Check if the specified character is not digit
            // then add this character into result variable
            if (!Character.isDigit(str.charAt(i))) {
                result = result + str.charAt(i);
            }
        }

        // Return result
        return result;
    }

    // Driver Code
    public static void main(String args[])
    {

        // Given alphanumeric string str
        String str = "GeeksForGeeks123";

        // Print the modified string
        System.out.println(removeAllDigit(str));
    }
}

Output

GeeksForGeeks

• Time Complexity: O(N)
• Auxiliary Space: O(N) 

Method 3: Using String.replaceAll() method

The idea is to use String.replaceAll() method that replaces all the sequence of characters that matches the given Regular Expression with the given replacement string.

Below is the implementation of the above approach:

Java

// Java program to remove all the
// digit from string
class GFG {

    // Function to remove all the digit
    // from string
    public static String removeAllDigit(String str)
    {
        // Replaces all the sequence of characters
        // that matches the given regex with
        // the given replacement string
        return str.replaceAll("\\d", "");
    }

    // Driver Code
    public static void main(String args[])
    {

        // Given alphanumeric string str
        String str = "GeeksForGeeks123";

        // Print the modified string
        System.out.println(removeAllDigit(str));
    }
}

Output

GeeksForGeeks

• Time Complexity: O(N)
• Auxiliary Space: O(1)